This invention relates generally to methods and apparatus for interactive display of computed tomographic (CT) images, and more particularly to methods and apparatus for display of such images in a limited amount of time to perform full volumetric analysis in a user-friendly manner.
In at least some computed tomography (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator adjacent the collimator, and photodetectors adjacent the scintillator.
CT, MR and XR routinely produce 3D data sets. Analyzing tortuous structures, such as airways, vessels, ducts or nerves is one of the major applications of these devices. Known methods and apparatus for accomplishing such analysis use multiple oblique slices to analyze local segments of these structures. The multiple oblique slice views provide clear, undistorted pictures of short sections of tortuous structures, but rarely encompass their full length.
Curved reformation images also provide synthetic views of tortuous structures, and advantageously capture the whole length of these objects. Thus, curved reformation images are well suited to analysis of such structures. True 3D length measurements along an axis of a tortuous structure can be obtained from these views, and measurements from these views are sufficiently close to the real anatomy in many cases.
In one known technique, curved reformation images are generated by sampling values along a curve at equidistant points to generate lines, and then translating the curve using a sampling vector to generate the next image line (i.e., along any 2D orientation). By representing the points in a polar coordinate system, with all of the points in the upper two quadrants of the coordinate system, a cubic spline algorithm is applied to a redefined set of points, thereby generating a series of functions that best approximates a desired curve. A conversion is then done to generate screen coordinates for selecting pixel values to display. Also, additional curves equidistant from an original curve are generated to produce additional views of the scanned structure. The calculation of these additional curves also uses a polar coordinate representation of cubic spline coefficients for the initial curve. These coefficients are used to determine intermediate data points at which a uniform length perpendicular is constructed. New data points equidistant from the initial curve are calculated by traversing each perpendicular a desired length.
Such known techniques and systems do not provide interactive adjustments well-suited to the display of tortuous structures. For example, in some known implementations, a curve is translated interactively but artifacts are created in the case of tortuous structures because the sampling curve may be outside of the object. These artifacts look like pseudo-stenoses.
To display some features, for example, bifurcations, local stenoses, and calcifications, one must manually redefine a sampling vector. This process is time consuming. Also, it is difficult to adjust the display to depict selected features. Also, the display assumes that the target features are known when the sampling vector is selected. Therefore, this known method is not practical for medical review because the possible lesions are not known ahead of time.
It would therefore be desirable to provide methods and apparatus for interactively displaying and adjusting the display of tortuous structures.
There is therefore provided, in a one embodiment of the present invention, a method for interactively rotating a sampling surface of a reconstructed computed tomographic (CT) image. The method includes steps of: scanning a volume of a patient to collect a plurality of slices of image data; displaying an image slice including a structure of interest on a display; defining a segmented line approximating a centerline of the structure of interest; selecting a rotation vector, a reference vector, and an angle; generating a sampling vector as a function of the rotation vector, the reference vector, and the selected angle; and generating a curved reformation image from the plurality of slices of image data using the segmented line and the sampling vector.
Embodiments of the present invention provide efficient interactive adjustments well suited to the display of tortuous structures. Embodiments of the present invention also do not require that the target features be known when a sampling vector is selected. Thus, such embodiments are practical for medical review when possible lesions are not known ahead of time.